NTM 4238-750Kv

[Andy.I]

I have a WOT Trainer with ac NTM 4238-750KV motor, and HK displays the following information:

LINK

The recommended props are either 13x10 or 14x6.

I was under the impression that one inch increase in pitch is equivalent to two inches in diameter. Can anybody comment on or explain the large difference in pitch between the two - or could it be a misprint and 13x10 should actually read 13x8 by any chance?

Edited By Andy.I on 21/07/2014 16:30:47

[Frank Skilbeck]

Not really, it all depends on how many cells you are using, I've run your motor and prop combo through www.drivecalc.de and you get the following

14 x 6 - 5s = 51A, 8566rpm, 3,350g static thrust

14 x 6 - 4s = 38A, 7485rpm, 2458g

13 x 10 - 4s = 48A, 6535rpm, 2,000g (but much higher top speed)

13 x 8 - 4s = 40A, 7432rpm, 2477g

But these don't compare with the prop data on the website so maybe they have done a misprint.

Edited By Frank Skilbeck on 22/07/2014 09:26:12

[Andy.I]

Thank you Frank

Things are slowly coming clear to me. Previously I used to run this motor on 4s with a wooden 13 x 8 which I seem to remember gave around 550W. I've just tried an APC 13x10 and I got 700W, 47A which agrees closely with your DriveCalc figures.

Having realised I was wrong about the approximate relationship between pitch and diameter (one inch increase in diameter actually being approximately equivalent to two inches in pitch) I now understand the jump between the two suggested props isn't as great as I thought and a 14 x 6 is actually going to draw less power, as is indeed indicated by your DriveCalc figures..

I'm perfectly happy with the current performance on 13 x 10 but I'm curious about efficiency and I'd also like to use a wooden prop. The motor is rated at 55A and I am using a 60A ESC so there is room for improvement; I think my next step should be to carefully test a 14 x 8. Does that make sense?

By the way, had anybody else got problems installing DriveCalc 3.4? I've tried several times and I get baffling messages about the database being missing, which is why I have never got around to using it, so if anybody could give me any tips please, I'd be grateful.

Edited By Andy.I on 23/07/2014 10:28:35

[Yobyid]

Obvious question - Did you Download the Database?

Les

[Andy.I]

I have tried to, but I get the message: "cannot commit - no transaction is active" and I if I hit "OK" the message reappears. There are four buttons displayed at the bottom of the Database update popup window but they are all greyed out except the Stop button.